This invention concerns a method for rapidly and accurately determining antioxidant levels in small samples of new and used hydrocarbonaceous materials by titration of antioxidant therein with peroxy radicals formed by agents that cause free radical oxidation acting on oxidizable substrates.
Routine analysis for antioxidant levels of food stuffs, fuels, lubricants, organic polymers and other hydrocarbonaceous materials is normally a difficult and tedious operation. Not only are the levels of antioxidants in hydrocarbonaceous materials very low, e.g., 1% by weight or less, but such antioxidants are also usually in complex admixture with other additives and/or decomposition products of the hydrocarbonaceous materials.
The method of this invention is specific for antioxidants which are free radical terminators and advantageously requires only very small samples for accurate determination of effective antioxidant levels.
Publications (disclosing methods) in which antioxidant levels are analyzed include: (1) "Determination of Diorgano Sulfide and Tertiary Phosphite Antioxidants in Polyolefins by Selective Oxidation with m-Chloroperoxybenzoic Acid" Kellum, Anal. Chem. 1971, 43(13), 1843-7, which discloses a step wise procedure for ascertaining levels of certain antioxidants, such step wise procedure not including measuring a rate of oxygen absorption; (2) "Determination of Antioxidant Activity of Cocoa Bean Shell Extract", Salmonowicz et al, Zesz Probl. Postepou Nauk Rolm., 1973, No. 136, 215-19 which discloses a comparative antioxidant analysis using thin-layer chromatography and comparative oxidation; (3) Hemoglobin Peroxidation Test Screens Antioxidants", Cost, Food Technol., 1974, 28(10), 60-6, which discloses use of oxygen absorption of aqueous emulsions; "Technique for Measuring Reactivity of Gasoline Antioxidants with Air" Strickland, Analytical Chemistry, 20, 55-56 (1948) which discloses an apparatus suitable for measuring oxygen absorption by systems comprising antioxidant; and "Possible Relation Between the Peroxide Number and Natural Antioxidants in Olive Oil" Incl. Agr., 6 (1), 21-24, 1968 which discloses iodometric method of analysis of antioxidant activity.